The present invention relates to the treatment of congestive heart failure using an external counterpulsation cardiac assist device which functions by applying positive and/or negative relative pressure to the limbs and more particularly, to the treatment of congestive heart failure using a relatively rigid, sealed housing for applying positive and/or negative relative (to atmospheric) pressure to the limbs in counterpulsation with heart function, which is adapted to be assembled in situ to provide customized fit and which requires reduced pumping capacity.
Congestive heart failure (CHF) has become a major public health problem. It is one of the leading causes of mortality. Approximately more than 5 million persons have CHF; the annual incidence is more than 550,000 cases; and CHF accounts for more than 900,000 hospital discharges a year. (See, “American Heart Association, Heart Disease and Stroke Statistics-2004 Update”, Dallas, American Heart Association, 2003.) The goals of therapy for patients with congestive heart failure (CHF) are to return the function of the left ventricle to normal, and to maintain a normal cardiac output. The benefits derived from pharmacologic interventions may be limited and become ineffective as the disease progresses. The implantation of a left ventricular assist device (LVAD) device may involve invasive major surgery, constant maintenance of a pump, and may modify the heart so that if the pump malfunctions the patient may not survive.
Congestive heart failure represents an enormous public health concern and is a leading cause of death. According to the American Heart Association there are an estimated 5 million Americans with congestive heart failure. Each year there are an estimated 550,000 new CHF cases. (See, “Heart Disease and Stroke Statistics-2004 Update”, 2003.) It is expected that the number will increase to 10,000,000 by the year 2037, which makes coronary artery disease a leading cause of permanent disability in the US work force. (See, Silver, M., Maisel, A., Yancy, C. W., McCullough, P. A., Burnett, J. C., Francis, G. S., Mehra, M. R., Peacock, W. F., Fonarow, G., Gibler, B., Morrow, D. A., Hollander, J. BNP Consensus Panel 2004; “A Clinical Approach For The Diagnostic, Prognostic, Screening, Treatment, And Monitoring, And Therapeutic Roles Of Natriuretic Peptides In Cardiovascular Disease”, Congestive Heart Failure, September-October, 2004, vol. 10, issue 5, supplement 3.)
The incidence of CHF is almost equal among men and women and the annual incidence is approximately 10 per thousand after 65 years of age. However, the incidence is twice as common among persons with hypertension and five times greater among persons who have had a heart attack. The incidence is 1.5 times higher among black men and women than among white men and women. While most of those with CHF are older; some 1.4 million are under 60 years of age.
Congestive heart failure accounts for more than 900,000 hospital discharges a year at a hospital cost of $18.8 billion. The direct and indirect cost of treating this disease has been estimated at $25.8 billion a year. (See, “Heart Disease and Stroke Statistics-2004 Update, 2003”.)
The incidence and prevalence of CHF as well as the costs associated with CHF will continue to increase as more cardiac patients live longer with their disease and thereby increase their risk to develop CHF. CHF may be the only form of heart disease that is increasing in the United States. And, it may continue to do so as more and more victims of coronary occlusions survive and their longevity is increased. However, with each such event the heart muscle is further injured and replaced by scar tissue, which decreases the ability of the left ventricle to perfuse the body. Thus, higher survival rates and increased longevity lead to an increased number of people surviving long enough for congestive heart failure to become likely.
Further, the continued growth in the number of older persons in the population will also result in increasing numbers of persons with this disease regardless of trends in coronary disease morbidity and mortality.
In 2001 some 50,000 people died of heart failure and it was a contributing factor in 266,000 deaths. CHF is the first-listed diagnosis in 875,000 hospitalizations and is the number one cause for hospitalization among individuals 65 years of age and older. (See, “Heart Disease and Stroke Statistics-2004 Update, 2003”.) The increasing prevalence of CHF and the resultant increase in hospitalizations and deaths have made CHF a major chronic condition in the United States that calls out for more effective treatment modalities that are also cost effective.
In light of the enormity of the CHF market, the last 20 years has seen the development of a wide variety of non-pharmacologic diagnostic and therapeutic devices and procedures. Nevertheless, the patient with heart failure remains inadequately helped. (See, Silver, M., et al.) An overwhelming need for new and better therapies exists.
Mechanical support of the failing left ventricle can be accomplished in two known ways. One known approach is the use of implantable mechanical devices to support circulation. These devices are usually aimed at the left ventricle (i.e., LVAD's) and have been primarily used for temporary short-term circulatory support and as a bridge to cardiac transplantation. The LVAD requires surgery to the heart to insert the device, and if the LVAD fails, support for the patient's heart is lost and leads to death of the patient. In addition, LVAD's have encountered the problem of blood clotting. At the same time, experience with LVAD's has shown success with some patients in the building of collaterals and the improvement of ventricular function to the point where some have not required heart transplants. This effect is most likely due to the reduction of afterload.
As pointed out above, support of the failing left ventricle can be accomplished by one of two approaches. In the first, an implanted pump removes the blood from the left ventricle and then returns it to the aorta as is the case with the left ventricular/aortic assist devices (LVAD). The second known approach is based on the studies by Soroff et al., that showed that when the pressure against which the left ventricle must work to eject its blood is lowered, the oxygen requirements and work of the left ventricle are significantly reduced. (See, Soroff, H S., Levine, H J., Sachs, B F., Birtwell, W C., Deterling, R A., “Effects of Counterpulsation on Left Ventricular Oxygen Consumption and Hemodynamics”, Circulation, Volume XXVII, April 1963.) This proved that if the pressure in the aorta (afterload) is reduced, the left ventricle can do the same work with less energy consumption. The equipment developed for the above studies, however, was invasive. The equipment utilized a cannula in the femoral artery to withdraw blood rapidly and return it. This method resulted in a great deal of hemolysis and was soon abandoned.
In 1967 the research group at Tufts University created a system that could produce a negative pressure of −50 mm Hg during cardiac systole as well as a positive pressure during cardiac diastole. The addition of the negative pressure phase enabled the system to assist patients with compromised or failing left ventricles. This system capable of producing negative pressure was evaluated in the treatment of 20 patients with severely compromised left ventricles and cardiogenic shock following myocardial infarctions. This treatment resulted in a significant reduction in the mortality rate for this group of patients. (See, Soroff H S, Cloutier C T., Birtwell W C., Begley L A., Messer J V., “External Counterpulsation.Management of Cardiogenic Shock After Myocardial Infarction”, J JAMA, 1974, 229(11), 1441-50.)
The second goal is to bring about an increase in cardiac output. This may result from an increased venous return. The positive pressure applied by the ELVAD may be minimal during the acute phase of the illness, and may gradually be increased to +50 to +100 mmHg. As the patient improves, the goal of increasing cardiac output to 20% over the pretreatment levels may be easily achieved as a result of increased venous return working in tandem with the decreased left ventricular afterload. This increase in cardiac output of 20% may significantly improve the patient's ability to perform the tasks of daily living.
A known method of assisting the circulation without invading the vascular system by the external application of intermittent pressure to the body has been known. Studies have shown that application of a positive relative pressure pulse to the lower extremities during cardiac diastole can raise the diastolic pressure by 40% to 50% while the application of negative relative pressure (vacuum), during cardiac systole can lower the systolic pressure by about 30%. Hereinafter, by “relative” pressure, it is meant relative to the atmospheric (gauge) pressure.
This externally applied positive and negative relative pressure increases the venous return to the heart because of the unidirectional valves in the peripheral venous bed. In cariogenic shock accompanied by myocardial ischemia, the increased coronary flow may improve cardiac function and thus indirectly affect the hemodynamic response to this procedure. Further, it is believed to promote the growth of collateral channel blood vessels feeding heart tissue and to reduce the symptoms of angina.
The therapeutic results of the known methods are well documented. However, as a practical matter, the apparatus used to externally apply positive and negative relative pressure to the limbs has been extremely inefficient and therefore the procedure has not found wide acceptance.
Early apparatus employed for this purpose included a prefabricated hinged conical metal housing or shell housing. Within the housing, a hollow cylindrical inflatable rubber balloon-like tube was placed, within which the limb segment was situated. The balloon-like rubber tube was filled with water, which was pressurized to inflate the tube, thereby filling the interior of the housing and applying pressure to the surface area of the limb segment.
To apply negative relative pressure, the water was first pumped out of the rubber tube, leaving an air gap between the rubber tube and the limb. An impermeable, rubber-like coated fabric was placed around the exterior of the housing, and was sealed around the limb to trap the air between the limb and the rubber tube. By pumping out the air trapped within the sealed fabric, the fabric first collapsed around the housing, and then negative pressure began to form within the gap between the limb and the rubber tube.
This system had numerous operational difficulties. Due to high resistance to flow, it was nearly impossible to pressurize the rubber tube and pump the water out of the rubber tube fast enough to match the heart beat. As the result, even the process of applying positive relative pressure was very difficult. The process was made even more difficult since a prefabricated housing could not be made to closely fit every patient, therefore a relatively large gap was left between the rubber tube and the limb to be filled by the expanding rubber tube. The amount of air that had to be pumped out of the rubber-coated fabric enclosed space around the housing and in between the limb and the rubber tube was relatively large, thereby requiring large air pumping action. In addition, due to the flexibility of the rubber-coated fabric, it would tend to deform and enter the space between the limb and the rubber tube, thereby making it difficult to achieve the desired level of negative pressure (vacuum) around the limb.
Current applicators utilize a prefabricated and relatively non-extensible fabric within which a balloon-like element is located. The balloon-like element with its enclosing housing or cuff is wrapped around the limb and secured by straps equipped with hook and loop tape, commercially known as VELCRO. Such applicators are currently available from Vassmedical, Inc. of Westbury, N.Y.
During its operation, the balloon is pressurized by air, thereby applying pressure to the surface of the enclosed limb. Due to the bulging and deformation of the cuff as the balloon is pressurized, a relatively large volume of air is required to achieve the required limb surface pressure. This is the case even though the cuff material is relatively non-extensible and the cuff is applied snugly to the limb segment. As the result, large capacity pumps are required to drive the apparatus because of the large volume of air which has to be rapidly moved in and in most cases out of the balloons, to alternatively inflate and deflate the balloons, to apply the required pressure to the limb. This and all variations of such applicator designs that use balloons to apply pressure, cannot be used to apply relative negative pressure to the limb. Another disadvantage of the current applicators is that due to the requirement of a large air volume, the system is rendered non-portable, and hence cannot be made available outside a fixed treatment room and cannot be available in emergency situations.
An attempt has recently been made to develop design concepts with a rigid or semi-rigid outer shell which surround an inflatable balloon-type interior. An applicator of this type is illustrated in U.S. Pat. No. 5,554,103 issued Sep. 10, 1996 to Zhang, et al. and U.S. Pat. No. 5,997,540 issued Dec. 7, 1999 to Zhang, et al., both of which are owned by Vasomedical, Inc. of Westbury, N.Y. Those applicators are described to be wrapped around the limb and held in place with some means such as straps of VELCRO. However, such prefabricated applicator designs cannot closely fit the limb and thus still require a large volume of air to provide the required limb surface pressure level. This is the case since such prefabricated applicators cannot be made to precisely fit a limb segment, thereby leaving a significant dead space between the balloon-like tube and the limb.
The aforementioned patents propose to fill the dead space by spacers to reduce the amount of air required for the operation of the applicator. These spacers have to be cut in various shapes and thicknesses and therefore are highly cumbersome and impractical.
The outer shells and applicators may be custom made to fit the limb segments. A large number of applicators of various sizes and shapes may also be fabricated to nearly accommodate the contour of the limbs of various patients. Custom made applicators are obviously impractical. The fabrication and hospital inventory of a large number of applicators of different sizes and shapes suitable for a wide variety of different size patients is also impractical.
In addition, since such applicators operate by pressurizing balloon-like tubes around the limb segment, they cannot be used to apply negative relative pressure to the limb segment.